Every fiber takes dye differently, so unfortunately it will require a lot of trial and error. In addition, dye concentration, pH, dyebath temperature and time in the dyebath all affect dye results. Optimum dyebath temperature is 185-200 degrees F, optimum pH is 3-4. Time in the dyebath is going to depend on the amount of fiber-a good deal of yardage might take 30-60 minutes, while you might get optimum penetration with a feather in maybe 10 minutes. A good dye amount is 3-6% by dry weight of the fiber.

If you think that some of your parameters didn't meet the specs above, you might want to redye with the Scarlet. If all of the specs were met, then you may want to move on to experimenting with another red such as #617 Cherry Red or #618 Fire Red.